1. Technical Field
The present invention relates to a gas laser resonator suitable for use with a laser machining apparatus employed to drill an object such as a printed circuit board by using a laser, for example.
2. Related Art
In a known structure of gas laser resonators, a pair of facing electrodes is arranged within an airtight container in which a laser medium gas is sealed and a plasma discharge is generated between the electrodes.
FIG. 15 is an exploded perspective view of such a gas laser resonator. In FIG. 15, inside a rectangular metal tube 1, a square discharge chamber 2 is formed extending from one end to the other end of the tube 1. Inside the discharge chamber 2, a pair of facing electrodes 3 and 4 is arranged. A bracket 6 is attached to one end of the tube 1 with a gasket 5 interposed for sealing, and a glass plate 8 and another bracket 9 are attached to the other end with another gasket 7 interposed for sealing. On the end faces of the tube 1 to which the gaskets 5 and 7 are contact are formed grooves in which the gaskets 5 and 7 are seated, as well known in this field. The discharge chamber 2 is sealed hermetically with a laser medium gas at a pressure of one-tenth of the atmospheric pressure, for example, as usually used in the discharge. The laser generated in the discharge chamber 2 is emitted through the glass plate 8 and emerged out of a window 10 provided in the bracket 9. Elements 11 are screws used for fixing the brackets 6 and 9 to the tube 1.
In such a gas laser resonator, there are problems resulting in a deterioration in quality of the plasma discharge, when a considerable time has elapsed after it has been manufactured, such as a change of the pressure in the interior of the discharge chamber 2 and an inflow of impurity gases, caused by leakage of air or the like into the discharge chamber 2 through imperfections of the gaskets 5 and 7.
For example, the gas laser resonator disclosed in U.S. Pat. No. 5,237,580 (FIG. 1) has the structure as shown in FIG. 15, and no consideration has been made to the problems of the change of the pressure in the discharge chamber and the inflow of impurity gases, caused by leakage of air or the like into the discharge chamber.